1. Field of the Invention
The present invention relates to a digital signal multiplex device having at least one multiplexer and at least one demultiplexer for pulse frames having a number of useful information channels, and in particular to such a device having an error protection coder and decoder.
2. Description of the Prior Art
Digital signal multiplex systems employing at least one multiplexer and at least one demultiplexer for pulse frames which have a number of useful information channels are described, for example, in the Special Issue/Digital Transmission of "Telcom-Report," 2 (1979) at pages 45-61 and 59-64. Pulse frames or formats for this purpose are described in the CCITT Yellow Book, Volume III, Fascicle III.3, "Digital Networks, Transmission Systems and Multiplexing Equipment," Recommendation G.751, pages 144-145.
In modern analog telecomunications networks, approximately ten percent of the transmission capacity is utilized for data transmission. A similar level may also be expected in future digital telecommunications networks. For purpose of economy, the transmission quality of the analog telecomunications networks has been adapted to the requirements of telephone traffic. Data transmission requires a considerably higher transmission quality than has heretofore been employed, the higher quality including, for example, coding and data protection in the terminal devices.
For the same reasons of economy, future digital telecommunications networks will also be adapted to the requirements of telephone traffic. For transmitting data signals and video signals, provisions will also be required in digital telecommunications networks to ensure the improved transmission quality required for such signals. It is possible to utilize known methods in association with data transmission for this purpose, such as an appropriately error-insenstive coding in the terminal device.
As described in "Coding for Error Correction and Error Recognition," Swoboda, 1973, data protection can be achieved by converting a source code into a redundant representation utilizing more binary digits. The coding of the information by code words having a fixed length of n digits is known as block coding. The n digits contain m information digits and k check or parity digits. The latter are determined on the basis of the m information digits in accordance with a predetermined rule, namely the error protection code. The receiver recognition and/or correction of faulty code words and the conversion of the information items into the original source code is referred to herein as decoding.
One such conventional error protection code is the so-called F code described in IEEE Transactions, IT-16 (1970) 9, pages 649-650.